Capacitive coupling plasma processing apparatus

ABSTRACT

A capacitive coupling plasma processing apparatus includes a process chamber configured to have a vacuum atmosphere, and a process gas supply section configured to supply a process gas into the chamber. In the chamber, a first electrode and a second electrode are disposed opposite each other. The second electrode includes a plurality of conductive segments separated from each other and facing the first electrode. An RF power supply is configured to apply an RF power to the first electrode to form an RF electric field within a plasma generation region between the first and second electrodes, so as to turn the process gas into plasma by the RF electric field. A DC power supply is configured to apply a DC voltage to at least one of the segments of the second electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 11/392,811,filed Mar. 30, 2006, the entire contents of which are incorporatedherein by reference. U.S. application Ser. No. 11/392,811, also claimsthe benefit of U.S. Provisional Application No. 60/666,699, filed Mar.31, 2005. This application is based upon and claims the benefit ofpriority from prior Japanese Patent Application No. 2005-102954, filedMar. 31, 2005, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma processing apparatus of thecapacitive coupling type, used for performing a plasma process on atarget substrate in, e.g., a semiconductor processing system. The term“semiconductor process” used herein includes various kinds of processeswhich are performed to manufacture a semiconductor device or a structurehaving wiring layers, electrodes, and the like to be connected to asemiconductor device, on a target substrate, such as a semiconductorwafer or a glass substrate used for an LCD (Liquid Crystal Display) orFPD (Flat Panel Display), by forming semiconductor layers, insulatinglayers, and conductive layers in predetermined patterns on the targetsubstrate.

2. Description of the Related Art

For example, in manufacturing semiconductor devices, plasma processes,such as etching, sputtering, and CVD (Chemical Vapor Deposition), areoften used for processing a target substrate or semiconductor wafer.There are various plasma processing apparatuses for performing suchplasma processes, but parallel-plate plasma processing apparatuses ofthe capacitive coupling type are the ones in mainstream use.

In general, a parallel-plate plasma etching apparatus of the capacitivecoupling type includes a process chamber with a pair of parallel-plateelectrodes (upper and lower electrodes) disposed therein. When a processis performed, while a process gas is supplied into the chamber, an RF(radio frequency) power is applied to one of the electrodes to form anRF electric field between the electrodes, thereby causing RF electricdischarge. The process gas is turned into plasma by the RF electricfield, thereby performing, e.g., plasma etching on a predetermined layerdisposed on a semiconductor wafer.

For example, there is an apparatus of this kind in which an RF power isapplied to the lower electrode on which the semiconductor wafer isplaced. In this case, the lower electrode serves as a cathode electrode,and the upper electrode serves as an anode electrode. The RF powerapplied to the lower electrode is used for plasma generation and alsofor an RF bias applied to the target substrate.

In the parallel-plate plasma processing apparatus of the capacitivecoupling type, the upper electrode serving as an anode electrode needsto be protected from metal contamination and wear-out. For this reason,the upper electrode is formed of a metal base body having a surfacecovered with a coating made of an oxide film or insulative ceramic withhigh resistance to plasma, such as Y₂O₃.

Plasma is generated by RF electric discharge caused between theelectrodes, and electron and ion currents generated thereby areneutralized at the ground potential. Accordingly, relative to the groundpotential, the insulating film covering the upper electrode comes tohave a potential, by which the plasma potential is determined.

In recent years, design rules in manufacturing semiconductor deviceshave been increasingly miniaturized. Particularly, in plasma etching, itis required to improve the dimensional accuracy, selectivity relative tothe mask and under-layer, and planar uniformity of the etching. For thisreason, the recent trend is to use a lower pressure and lower ion energyin the process field within a chamber. This trend has brought about theuse of an RF power with a frequency of 27 MHz or more, which is farhigher than the frequency conventionally used.

However, where a lower pressure and lower ion energy are used, asdescribed above, it becomes necessary to address a decrease in theplanar uniformity of plasma potential, which previously had beennegligible. Specifically, in conventional apparatuses using high ionenergy, poor planar uniformity of plasma potential does not cause aserious problem. However, as the pressure and ion energy are set to belower, poor planar uniformity of plasma potential can easily make theprocess less uniform and easily cause charge-up damage.

In this respect, U.S. Pat. No. 6,624,084 (Patent Document 1) discloses atechnique concerning a plasma processing apparatus. Specifically, thisdocument discloses a technique of improving the planar uniformity ofself-bias on a wafer generated by RF bias application, to reduce microdefects, such as charge-up damage. In order to achieve this, currentpath reform means is disposed for that portion of the RF current path ofthe RF bias applied to the wafer that is close to the periphery of thewafer, to cause an RF current to flow toward the surface of the counterelectrode facing the wafer. Alternatively, impedance adjusting means isused to cause the impedance from the RF bias to ground to be almostuniform planarly on the wafer.

However, the technique of Patent Document 1 requires the current pathreform means or impedance adjusting means and thus makes the apparatusstructure complicated. Further, this technique is not necessarilysufficient in the planar uniformity of plasma processing.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention to provide a plasma processingapparatus of the capacitive coupling type, which brings about a highplanar uniformity of plasma processing, and prevents charge-up damage.

According to a first aspect of the present invention, there is provideda capacitive coupling plasma processing apparatus comprising:

a process chamber configured to have a vacuum atmosphere;

a process gas supply section configured to supply a process gas into thechamber;

a first electrode disposed in the chamber;

a second electrode disposed opposite the first electrode in the chamber,and comprising a plurality of conductive segments separated from eachother and facing the first electrode;

a support member configured to support the target substrate between thefirst and second electrodes such that a process target surface of thetarget substrate faces the second electrode,

an RF power supply configured to apply an RF power to the firstelectrode to form an RF electric field within a plasma generation regionbetween the first and second electrodes, so as to turn the process gasinto plasma by the RF electric field; and

a DC power supply configured to apply a DC voltage to at least one ofthe segments of the second electrode.

According to a second aspect of the present invention, there is provideda capacitive coupling plasma processing apparatus comprising:

a process chamber configured to have a vacuum atmosphere;

a process gas supply section configured to supply a process gas into thechamber;

a first electrode disposed in the chamber and configured to support atarget substrate thereon;

a second electrode disposed opposite the first electrode in the chamber,and comprising an inner segment and an outer segment disposed around andseparated from the inner segment,

an RF power supply configured to apply an RF power to the firstelectrode to form an RF electric field within a plasma generation regionbetween the first and second electrodes, so as to turn the process gasinto plasma by the RF electric field; and

a DC power supply configured to apply a DC voltage to at least one ofthe inner segment and the outer segment, such that the DC voltage of theDC power supply is applied to cause the inner segment to have anelectric potential higher than that of the outer segment.

In the apparatus according to the first and second aspects, the spatialelectric potential distribution is uniformized, so that the substratereceives ion energy incident thereon with a uniform distribution.Further, the uniform ion energy brings about uniform electron energy inplasma generation, thereby resulting in a uniform electron densitydistribution. Consequently, it is possible to improve the planaruniformity of the etching process, and to reduce the charge-up damage,such as dielectric breakdown of gate oxide films.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a sectional view showing a plasma etching apparatus or plasmaprocessing apparatus according to an embodiment of the presentinvention;

FIG. 2 is a view schematically showing a plan view layout of an innersegment and an outer segment used in the upper electrode of the plasmaetching apparatus shown in FIG. 1;

FIG. 3 is a sectional view schematically showing a structure where an RF(radio frequency) power supply for plasma generation and an RF powersupply for ion attraction are connected to a lower electrode used as asupport table;

FIG. 4 is a view schematically showing the structure of an electrodeplate used as an upper electrode in a conventional plasma etchingapparatus;

FIG. 5 is a view showing electron density distribution and plasmapotential distribution in plasma where the conventional plasma etchingapparatus is used;

FIG. 6 is a view schematically showing a system for applying a DC(direct current) voltage to the segments used in the plasma etchingapparatus shown in FIG. 1;

FIGS. 7A and 7B are views schematically showing modifications of asystem for applying a DC voltage to the segments usable in the plasmaetching apparatus shown in FIG. 1;

FIG. 8 is a view schematically showing an alternative modification of asystem for applying a DC voltage to the segments usable in the plasmaetching apparatus shown in FIG. 1;

FIG. 9 is a view schematically showing a further alternativemodification of a system for applying a DC voltage to the segmentsusable in the plasma etching apparatus shown in FIG. 1;

FIG. 10 is a view schematically showing a plan view layout of segmentsused in the upper electrode of a plasma etching apparatus or plasmaprocessing apparatus according to another embodiment of the presentinvention;

FIG. 11 is a view schematically showing a system for applying a DCvoltage to the segments used in the plasma etching apparatus accordingto the embodiment shown in FIG. 10;

FIGS. 12A, 12B, and 12C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 200 W, the inner segment was grounded, andthe outer segment was supplied with the DC voltage at different voltagevalues;

FIGS. 13A, 13B, and 13C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 200 W, the outer segment was grounded, andthe inner segment was supplied with the DC voltage at different voltagevalues;

FIGS. 14A, 14B, and 14C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 500 W, the inner segment was grounded, andthe outer segment was supplied with the DC voltage at different voltagevalues;

FIGS. 15A, 15B, and 15C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 500 W, the outer segment was grounded, andthe inner segment was supplied with the DC voltage at different voltagevalues;

FIGS. 16A, 16B, and 16C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 800 W, the inner segment was grounded, andthe outer segment was supplied with the DC voltage at different voltagevalues;

FIGS. 17A, 17B, and 17C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 800 W, the outer segment was grounded, andthe inner segment was supplied with the DC voltage at different voltagevalues;

FIGS. 18A, 18B, and 18C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 1,200 W, the inner segment was grounded,and the outer segment was supplied with the DC voltage at differentvoltage values;

FIGS. 19A, 19B, and 19C are views showing the planar distribution ofplasma potential Vf, planar distribution of self-bias voltage Vdc, andplanar distribution of electron density distribution Ne, respectively,where the RF power was set at 1,200 W, the outer segment was grounded,and the inner segment was supplied with the DC voltage at differentvoltage values;

FIGS. 20A and 20B are views showing planar distribution of plasmapotential Vf, where the RF power was set at 200 W and 500 W,respectively, and the inner segment was supplied with the DC voltage atdifferent voltage values while no voltage was applied from adistribution control power supply; and

FIG. 21 is a view schematically showing another example of an upperelectrode.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. In the following description,the constituent elements having substantially the same function andarrangement are denoted by the same reference numerals, and a repetitivedescription will be made only when necessary.

FIG. 1 is a sectional view showing a plasma etching apparatus as aplasma processing apparatus according to an embodiment of the presentinvention.

This plasma etching apparatus 100 includes an airtight process chamber 1having an essentially cylindrical shape. For example, the chamber 1 hasa main body made of a metal, such as aluminum, with an inner surfacecovered with an insulating film formed thereon, such as an oxidizationprocessed film, or insulative ceramic film of, e.g., Y₂O₃ (for example,a thermal spraying film). The chamber 1 is grounded.

A support table 2 is disposed in the chamber 1 and configured tohorizontally support a target substrate or wafer W and to also serve asa lower electrode. For example, the support table 2 is made of aluminumwith an oxidization processed surface. A support portion 3 having a ringshape extends upward from the bottom of the chamber 1 at a positioncorresponding to the periphery of the support table 2. An insulatingmember 4 having a ring shape is disposed on the support portion 3, tosupport the periphery of the support table 2. Further, a focus ring 5made of a conductive material or insulative material is placed on theperiphery of the top of the support table 2. A baffle plate 14 isdisposed between the insulating member 4 and the wall of the chamber 1.An inner void 7 is formed between the support table 2 and the bottom ofthe chamber 1.

The support table 2 is provided with an electrostatic chuck 6 on the topsurface, for holding a wafer W by an electrostatic attraction force. Theelectrostatic chuck 6 comprises an electrode 6 a and a pair ofinsulating layers 6 b sandwiching the electrode 6. The electrode 6 isconnected to a DC (direct current) power supply 13 through a switch 13a. The semiconductor wafer W is attracted and held by an electrostaticforce, e.g., a Coulomb force, generated by a voltage applied from the DCpower supply 13 to the electrode 6 a.

A cooling medium passage 8 a is formed in the support table 2, and isconnected to cooling medium lines 8 b. A suitable cooling medium issupplied and circulated within the cooling medium passage 8 a from acooling medium control unit 8 through the cooling medium lines 8 b tocontrol the support table 2 at a suitable temperature. Further, a heattransmission gas line 9 a is disposed to supply a heat transmission gas,such as He gas, into the interstice between the top surface of theelectrostatic chuck 6 and the bottom surface of the wafer W. The heattransmission gas is supplied from a heat transmission gas supply unit 9through the gas line 9 a to the bottom surface of the wafer W.Consequently, even when the interior of the chamber 1 is exhausted andmaintained in a vacuum state, cold of the cooling medium circulated inthe cooling medium passage 8 a is efficiently transmitted, therebyimproving the temperature control of the wafer W.

A power feed line 12 for supplying an RF (radio frequency) power isconnected near the center of the support table 2. The power feed line 12is connected to a matching unit 11 and an RF power supply 10. The RFpower supply 10 is configured to apply an RF power with a predeterminedfrequency to the support table 2.

On the other hand, a disk-like showerhead 18 used as an upper electrode(thus which will be also referred to as an upper electrode 18) isdisposed above and opposite the support table 2. The showerhead 18 isfitted in the ceiling of the chamber 1. The showerhead 18 includes amain body 18 a made of a metal or semiconductor, such as carbon or Si.The surface of the main body 18 a facing the support table 2 is coveredwith an insulating film 18 b for preventing metal contamination,wear-out due to plasma, and generation of scratches. Further, theinsulating film 18 b is covered with an inner segment 18 _(c1) and anouter segment 18 _(c2), which are conductive and concentricallyseparated on the inner and outer sides, respectively. FIG. 2 is a viewschematically showing a plan view layout of the inner segment 18 _(c1)and outer segment 18 _(c2) used in the upper electrode 18 of the plasmaetching apparatus shown in FIG. 1. The insulating film 18 b is formed ofan oxidization processed film, or insulative ceramic film of, e.g., Y₂O₃(for example, a thermal spraying film).

A number of gas delivery holes 17 are formed to penetrate a lowerportion of the main body 18 a, the insulating film 18 b, and segments 18_(c1) and 18 _(c2). The gas delivery holes 17 communicate with a space18 e formed in the main body 18 a and a gas supply port 18 d formed atthe top of the main body 18 a. The gas supply port 18 d is connectedthrough a gas supply line 15 a to a process gas supply unit 15 forsupplying a process gas for etching.

The main body 18 a of the upper electrode 18 is grounded through thechamber 1 and cooperates with the lower electrode or support table 2supplied with an RF power, to define a pair of parallel-plateelectrodes. The lower electrode or support table 2 supplied with an RFpower serves as a cathode electrode, while the grounded upper electrode18 serves as an anode electrode. A plasma generation region for turningthe process gas into plasma is defined between the upper electrode 18and support table 2.

The inner segment 18 _(c1) and outer segment 18 _(c2) are connected tovariable DC power supply 30 to apply a DC voltage therebetween.Specifically, the inner segment 18 _(c1) is connected to the positiveterminal, and the outer segment 18 _(c2) is connected to the negativeterminal. The variable DC power supply 30 is connected to the innersegment 18 _(c1) through a feed line 30 a provided with a low-passfilter (LPF) 31 and a relay switch 32. The variable DC power supply 30is connected to the outer segment 18 _(c2) through a feed line 30 bprovided with a low-pass filter (LPF) 33 and a relay switch 34. Theinner segment 18 _(c1) and outer segment 18 _(c2) serve to supply avoltage to the plasma space. The inner segment 18 _(c1) and outersegment 18 _(c2) can be formed by various methods including filmformation techniques, such as bonding, thermal spraying, and CVD. Thevariable DC power supply 30 is preferably formed of a bipolar powersupply.

The process gas for etching can be selected from various conventionalprocess gases, and it may be a gas containing a halogen element, such asa fluorocarbon gas (C_(x)F_(y)) or hydrofluorocarbon gas (CpHqF_(r)).The process gas may further contain a rare gas, such as Ar or He, N₂gas, or O₂ gas. Where the process gas is used for ashing, the processgas may be, e.g., O₂ gas.

The process gas is supplied from the process gas supply unit 15 throughthe gas supply line 15 a and gas supply port 18 d into the space 18 einside the main body 18 a. Then, the process gas is delivered from thegas delivery holes 17 and used for etching a film formed on the wafer W.

The bottom of the chamber 1 is connected through an exhaust line 19 toan exhaust unit 20 including a vacuum pump or the like. The exhaust unit20 is configured to reduce the pressure inside the chamber 1 to apredetermined vacuum level by the vacuum pump. A transfer port 23 forthe wafer W is formed in the upper portion of the sidewall of thechamber 1, and is opened/closed by a gate valve 24 attached thereon.

On the other hand, two ring magnets 21 a and 21 b are disposed coaxiallyaround the chamber 1 at positions above and below the transfer port 23of the chamber 1. The ring magnets 21 a and 21 b are configured to forma magnetic field around the process space between the support table 2and upper electrode 18. The ring magnets 21 a and 21 b are rotatable bya rotation mechanism (not shown).

In each of the ring magnets 21 a and 21 b, a plurality of segmentmagnets formed of permanent magnets are disposed to be a ring in amulti-pole state. Specifically, in each of the ring magnets 21 a and 21b, the magnetic poles of adjacent segment magnets are oriented inopposite directions. Consequently, magnetic force lines are formedbetween adjacent segment magnets, such that a magnetic field of, e.g.,0.02 to 0.2 T (200 to 2000 Gauss), and preferably of 0.03 to 0.045 T(300 to 450 Gauss), is formed only around the process space, whileessentially no magnetic field is formed at the position where the waferis placed. Consequently, it is possible to obtain a suitable effect ofconfining plasma. It should be noted that “essentially no magnetic fieldis formed at the position where the wafer is placed” is not limited to acase where no magnetic field is present. For example, this conceptincludes a case where a magnetic field is formed at the position wherethe wafer is placed, but the magnetic field has essentially no effect onthe plasma process.

In order to adjust the plasma density and ion attraction, an RF powerfor plasma generation may be superposed with an RF power for ionattraction from plasma. Specifically, as shown in FIG. 3, in addition tothe RF power supply 10 for plasma generation connected to the matchingunit 11, an RF power supply 26 for ion attraction is connected to amatching unit 11 b to superpose the RF powers. In this case, the RFpower supply 10 for plasma generation 10 is preferably set to have afrequency within a range of 27 MHz to 160 MHz. The RF power supply 26for ion attraction is preferably set to have a frequency within a rangeof 500 KHz to 27 MHz. With this arrangement, ion energy can becontrolled to further increase the plasma processing rate, such as anetching rate.

The respective components of the plasma etching apparatus 100 areconnected to the control section (process controller) 50 and controlledthereby. Specifically, the control section 50 is configured to controlthe cooling medium control unit 8, the heat transmission gas supply unit9, the exhaust unit 20, the switch 13 a of the DC power supply 13 forthe electrostatic chuck 6, the RF power supply 10, and the matching unit11.

The control section 50 is connected to a user interface 51 including,e.g., a keyboard and a display, wherein the keyboard is used for aprocess operator to input commands for operating the plasma etchingapparatus 100, and the display is used for showing visualized images ofthe operational status of the plasma processing apparatus 100.

Further, the control section 50 is connected to a storage section 52that stores control programs for the control section 50 to control theplasma etching apparatus 100 so as to perform various processes, andprograms or recipes for respective components of the plasma etchingapparatus 100 to perform processes in accordance with processconditions. Recipes may be stored in a hard disk or semiconductormemory, or stored in a portable storage medium, such as a CDROM or DVD,to be attached to a predetermined position in the storage section 52.

A required recipe is retrieved from the storage section 52 and executedby the control section 50 in accordance with an instruction or the likethrough the user interface 51. As a consequence, the plasma etchingapparatus 100 can perform a predetermined process under the control ofthe control section 50.

Next, an explanation will be given of a process operation of the plasmaetching apparatus having the structure described above.

At first, the gate valve 24 of the plasma etching apparatus 100 shown inFIG. 1 is opened, and a wafer W having a layer to be etched istransferred into the chamber 1 and placed on the support table 2 by atransfer arm. After the transfer arm is retreated therefrom and the gatevalve 24 is closed, the interior of the chamber 1 is exhausted by thevacuum pump of the exhaust unit 20 through the exhaust line 19 to setthe pressure inside the chamber 1 to be a predetermined vacuum level.

Thereafter, a process gas for etching is supplied from the process gassupply unit 15 into the chamber 1 at a predetermined flow rate, so thatthe pressure inside the chamber 1 is set to be a predetermined valuewithin a range of, e.g., about 0.13 to 133.3 Pa (1 to 1,000 mTorr).While the chamber 1 is maintained at a predetermined pressure, an RFpower with a frequency of 27 MHz or more, such as 100 MHz, is appliedfrom the RF power supply 10 to the support table 2. At the same time, apredetermined voltage is applied from the DC power supply 13 to theelectrode 6 a of the electrostatic chuck 6 to attract and hold the waferW by, e.g., a Coulomb force.

With the RF power applied to the lower electrode or support table 2 asdescribed above, an RF electric field is formed in the process space(plasma generation region) between the upper electrode or showerhead 18and the lower electrode or support table 2. The process gas suppliedinto the process space is turned into plasma by the RF electric field,and the etching target layer on the wafer W is etched by the plasma.

During this etching, a magnetic field is formed around the process spaceby the ring magnets 21 a and 21 b configured in a multi-pole state. Thismagnetic field brings about the effect of confining the plasma to makethe plasma more uniform, even where the apparatus employs an RF powerwith a frequency that tends to generate less uniform plasma as in thisembodiment. The magnetic field may have no effect, depending on the typeof the film, but, in such a case, the segment magnets can be rotated toform essentially no magnetic field around the process space during theprocess.

When the magnetic field is formed, the conductive or insulative focusring 5 disposed around the wafer W on the support table 2 enhances theeffect of making the plasma process more uniform. Specifically, wherethe focus ring 5 is made of a conductive material, such as silicon orSiC, the area serving as a lower electrode expands to the focus ring.Consequently, the plasma generation region is enlarged to a positionabove the focus ring 5, and the plasma generation is promoted on theperipheral portion of the wafer W, thereby improving the etching rate tobe more uniform.

Where the focus ring 5 is made of an insulative material, such asquartz, the focus ring 5 cannot transfer electric charges to and fromelectrons and ions in plasma. In this case, the effect of confiningplasma is enhanced, thereby improving the etching rate to be moreuniform.

As described above, the counter surface of the upper electrode 18 iscovered with the conductive inner segment 18 _(c1) and outer segment 18_(c2), and the planar uniformity of the electric field is therebyimproved on this conductive counter surface, so the plasma process onthe wafer W is improved to be more uniform. A detailed explanation onthis matter will be given below.

FIG. 4 is a view schematically showing the structure of an electrodeplate used as an upper electrode in a conventional plasma etchingapparatus. Conventionally, as shown in FIG. 4, the surface of the mainbody 18 a of an upper electrode 18 is covered with an insulating film 18b formed thereon, such as an oxidization processed film, or insulativeceramic film of, e.g., Y₂O₃ (for example, a thermal spraying film), forpreventing metal contamination and wear-out due to plasma. In this case,the insulating film 18 b is the outermost layer, and thus that surfaceof the upper electrode 18 which is exposed to the plasma generationregion is an insulative surface (i.e., the counter surface of the upperelectrode 18 is covered with the insulative surface). Further, the innersurface of the chamber 1 is also covered with a similar insulating film.

FIG. 5 is a view showing electron density distribution and plasmapotential distribution in plasma where the conventional plasma etchingapparatus is used. In this apparatus, as shown in FIG. 5, when RF plasmais generated, an RF current flows through the insulating film 18 b onthe surface of the upper electrode 18 into the main body 18 a, butscarcely flows in the radial direction (planar direction) in the surfaceof the insulating film 18 b. With the RF plasma, the insulating film 18b on the surface of the upper electrode 18 comes to have a certainpotential distribution in the radial direction, because of, e.g., a pooruniformity of electron density distribution. In this case, the potentialdistribution remains uneven, and the plasma potential comes to have apoor planar uniformity. Consequently, the support table 2 serving as acathode electrode or lower electrode receives ion energy incidentthereon with a certain planar distribution, thereby deteriorating theplanar uniformity of wafer etching.

The conventional technique uses an RF power supply for plasma generationwith a frequency of 27 MHz or less and a high process pressure (about 2to 10 Pa) to generate plasma with high ion energy. In this case, even ifthe electrode surface has a certain potential distribution in the radialdirection, as described above, no problem is caused. However, some ofthe recent techniques use an RF power supply with a frequency or 27 MHzor more and a low pressure (1.3 Pa or less) to from plasma with a lowelectron density (1×10¹⁰/cm³ or less), and also use a negative gas as aprocess gas. In this case, the plasma has a high resistivity and thusmakes the process uniformity poorer. Further, in order to improve theprocess performance, it is necessary to perform control at low ionenergy (100 eV or less). In this case, a poor uniformity of energy dueto a poor planar uniformity of the plasma potential cannot be ignored.Specifically, dielectric breakdown (charge-up damage) of a gate oxidefilm may be caused by a poor planar uniformity of the plasma etchingprocess and a poor uniformity of charge-up on the wafer.

On the other hand, the upper electrode 18 of this embodiment isarranged, as shown in FIG. 6, in order to solve the problems describedabove. FIG. 6 is a view schematically showing a system for applying a DCvoltage to the segments used in the plasma etching apparatus shown inFIG. 1. Specifically, the surface of the main body 18 a facing thesupport table 2 is covered with the insulating film 18 b, on which theconductive inner segment 18 _(c1) and outer segment 18 _(c2) aredisposed concentrically and separately in the radial direction. Theinner segment 18 _(c1) and outer segment 18 _(c2) are respectivelyconnected to the positive terminal and negative terminal of the variableDC power supply 30.

In this embodiment, when RF plasma is generated, a voltage is appliedbetween the inner segment 18 _(c1) and outer segment 18 _(c2). In thiscase, the plasma generation space is supplied with a voltage, to controlthe spatial electric potential distribution. Specifically, the spatialelectric potential distribution shown in FIG. 5 can be changed such thatthe electric potential is increased more on the inner segment 18 _(c1)than on the outer segment 18 _(c2) to uniformize the spatial electricpotential distribution. In FIG. 6, arrows I denote electric currentflows in the plasma space due to the voltage application. The directionof this current becomes opposite where the polarity of the DC powersupply is reversed.

As described above, the spatial electric potential distribution isuniformized, so that the support table 2 serving as the lower electrodeor cathode electrode receives ion energy incident thereon with a uniformdistribution. Further, the uniform ion energy brings about uniformelectron energy in plasma generation, thereby resulting in a uniformelectron density distribution. Consequently, it is possible to improvethe planar uniformity of the etching process, and to reduce thecharge-up damage, such as dielectric breakdown of gate oxide films. Inaddition, the variable DC power supply 30 is formed of a bipolar powersupply, which can control the potential distribution within a range froma convex shape to a concave shape. In this case, it suffices if the DCvoltage applied between the inner segment 18 _(c1) and outer segment 18_(c2) is several tens of volts.

Even where one of the segments is supplied with a DC voltage, if theother segment is in a completely floating state, no electric potentialdifference is formed therebetween, and thus the effect described abovecannot be obtained. A current derived from the applied DC voltage flowsfrom the inner segment 18 _(c1) through plasma into outer segment 18_(c2), so abnormal electric discharge can be hardly caused, and a memberfor grounding is unnecessary.

The feed lines 30 a and 30 b connected to the variable DC power supply30 are respectively provided with the low-pass filters (LPFs) 31 and 33to remove the RF influence on the variable DC power supply 30. The feedlines 30 a and 30 b are further provided with the relay switches 32 and34 to turn on and off the DC voltage applied to the inner segment 18_(c1) and outer segment 18 _(c2). The relay switches 32 and 34 arepreferably disposed on the side closer to plasma from the low-passfilters (LPFs) 31 and 33, as shown in FIG. 6. If the relay switches 32and 34 are disposed on the side closer to the variable DC power supply30 from the low-pass filters (LPFs) 31 and 33, the following problemarises when no DC voltage is applied to the segments. Specifically, whenthe relay switches 32 and 34 are in the OFF-state, an RF power fromplasma may pass through the low-pass filters, thereby changing theplasma state inside the chamber 1. This matter is common to all thefollowing embodiments.

The material of the inner segment 18 _(c1) and outer segment 18 _(c2) isnot limited to a specific one, as long as it is conductive. Since thesegments are required only to supply a voltage to the plasma space, theyare allowed to have a somewhat high resistivity, as high as 1×10⁶ Ωcm,which allows the use of, e.g., Si or SiC. Further, even where thesurface state varies to some extent, the effect described above ismaintained.

According to this embodiment, the conductive inner segment 18 _(c1) andouter segment 18 _(c2) are formed on the insulating film 18 bconventionally used for a protection function, and thus the advantagesdescribed are obtained in addition to the conventional protectionfunction. Further, since the conductive layers are formed on aconventional upper electrode, the apparatus structure does not need tobe greatly changed.

FIGS. 7A and 7B are views schematically showing modifications of asystem for applying a DC voltage to the segments usable in the plasmaetching apparatus shown in FIG. 1. In the structure shown in FIG. 6, theinner segment 18 _(c1) and outer segment 18 _(c2) are in a floatingstate except for the connection to the variable DC power supply 30. Inthe modification shown in FIG. 7A, the outer segment 18 _(c2) isgrounded. In the modification shown in FIG. 7B, the inner segment 18_(c1) is grounded. As shown in these modifications, where one of thesegments is grounded, the spatial electric potential on the non-groundedside is largely adjustable while the spatial electric potential on thegrounded side is not changed so much.

FIG. 8 is a view schematically showing an alternative modification of asystem for applying a DC voltage to the segments usable in the plasmaetching apparatus shown in FIG. 1. In the modification shown in FIG. 8,another variable DC power supply 40 is connected to one of the segment,in addition to the variable DC power supply 30 for controlling thespatial electric potential distribution. In FIG. 8, the variable DCpower supply 40 is connected to the outer segment 18 _(c2), but it maybe connected to the inner segment 18 _(c1). As in this modification,where one of the segments is connected to the variable DC power supply40, the degree of the spatial electric potential (the potentialdifference between the plasma and electrode main body 18 a) can beadjusted while the spatial electric potential distribution ismaintained. Since the distribution and degree of the spatial electricpotential are adjustable, the ion energy relative to the wafer W can becontrolled with high accuracy. Further, since the degree of the spatialelectric potential is adjustable, the deposition onto the upperelectrode 18 can be controlled. Furthermore, since the degree of thespatial electric potential itself is adjustable by the variable DC powersupply 40, the variable DC power supply 30 for distribution control isnot required to apply a high voltage and thus this power supply can becompact.

FIG. 9 is a view schematically showing a further alternativemodification of a system for applying a DC voltage to the segmentsusable in the plasma etching apparatus shown in FIG. 1. In themodification shown in FIG. 9, the inner segment 18 _(c1) is connected toa variable DC power supply 42, and the outer segment 18 _(c2) isconnected to another variable DC power supply 44. With this arrangement,the voltages applied to the inner segment 18 _(c1) and outer segment 18_(c2) can be independently controlled from each other.

FIG. 10 is a view schematically showing a plan view layout of segmentsused in the upper electrode of a plasma etching apparatus or plasmaprocessing apparatus according to another embodiment of the presentinvention. FIG. 11 is a view schematically showing a system for applyinga DC voltage to the segments used in the plasma etching apparatusaccording to the embodiment shown in FIG. 10.

This embodiment includes an upper electrode 18 in which three segments18 _(c3), 18 _(c4), and 18 _(c5) are concentrically disposed in thisorder from the inner side on the surface of an insulating film 18 b. Theoutermost segment 18 _(c5) is connected to the negative terminal of avariable DC power supply 30 through a feed line 30 d. The middle segment18 _(c4) and innermost segment 18 _(c3) are connected to the positiveterminal of the variable DC power supply 30 respectively through feedlines 30 e and 30 f branched from a feed line 30 c. The feed lines 30 eand 30 f are respectively provided with relay switches 36 and 37, sothat the positive terminal of the variable DC power supply 30 can beconnected to either or both of the segments 18 _(c3) and 18 _(c4). Thefeed line 30 c is provided with a low-pass filter (LPF) 35. The feedline 30 d is provided with a low-pass filter (LPF) 38 and a relay switch39 for turning on and off the DC voltage.

With this arrangement, the segments to be supplied with the voltage canbe selected by switching. The spatial electric potential distributioncan be adjusted at a selected position, thereby improving theflexibility in controlling the spatial electric potential distribution.

Next, an explanation will be given of experiments performed to confirmadvantages of the present invention.

At first, an upper electrode was prepared such that the counter surfaceof a main body was covered with a 250 μm thermal spraying film of Y₂O₃,and an inner segment and an outer segment both made of Si wereconcentrically disposed on the film. A plasma process was performed on awafer, while one of the inner segment and outer segment was grounded,and the other was supplied with a predetermined DC voltage. The waferwas a 300-mm wafer, and the upper electrode had a diameter of 340 mm.The inner segment had a radius of 100 mm, and the outer segment had anouter radius of 180 mm. The plasma process was performed in theapparatus shown in FIG. 1, under the conditions of: the pressure insidethe chamber was set at 0.67 Pa, the process gas was O₂ gas with a flowrate of 200 mL/min, and the RF power was set to be with a frequency of100 MHz at different power levels of 200 W, 500 W, 800 W, and 1,200 W.At this time, the planar distribution of plasma potential Vf relative tothe ground potential (GND), planar distribution of self-bias voltageVdc, and planar distribution of electron density distribution Ne weremeasured.

FIGS. 12A, 12B, and 12C to FIGS. 19A, 19B, and 19C show data obtained inthis experiment. FIGS. 12A, 12B, and 12C shows a case where the RF powerwas set at 200 W, the inner segment was grounded, and the outer segmentwas supplied with the DC voltage at different voltage values of +40V,+20V, OV, and −80V. FIGS. 13A, 13B, and 13C shows a case where the RFpower was set at 200 W, the outer segment was grounded, and the innersegment was supplied with the DC voltage at different voltage values of+40V, OV, −2.2V, and −80V.

FIGS. 14A, 14B, and 14C shows a case where the RF power was set at 500W, the inner segment was grounded, and the outer segment was suppliedwith the DC voltage at different voltage values of +50V, OV, −50V, and−100V. FIGS. 15A, 15B, and 15C shows a case where the RF power was setat 500 W, the outer segment was grounded, and the inner segment wassupplied with the DC voltage at different voltage values of +40V, OV,−36.8V, and −50V. FIGS. 16A, 16B, and 16C shows a case where the RFpower was set at 800 W, the inner segment was grounded, and the outersegment was supplied with the DC voltage at different voltage values of+40V, +11.5V, OV, and −80V. FIGS. 17A, 17B, and 17C shows a case wherethe RF power was set at 800 W, the outer segment was grounded, and theinner segment was supplied with the DC voltage at different voltagevalues of +10V, OV, −19.8V, and −60V. FIGS. 18A, 18B, and 18C shows acase where the RF power was set at 1,200 W, the inner segment wasgrounded, and the outer segment was supplied with the DC voltage atdifferent voltage values of +10V, OV, −18.6V, and −60V. FIGS. 19A, 19B,and 19C shows a case where the RF power was set at 1,200 W, the outersegment was grounded, and the inner segment was supplied with the DCvoltage at different voltage values of +15V, +5.6V, OV, and −60V.

FIGS. 12A, 13A, 14A, 15A, 16A, 17A, 18A, and 19A show the planardistribution of plasma potential Vf, wherein ΔVf denotes planarfluctuation of Vf.

FIGS. 12B, 13B, 14B, 15B, 16B, 17B, 18B, and 19B show the planardistribution of self-bias voltage Vdc, wherein ΔVdc denotes planarfluctuation of Vdc.

FIGS. 12C, 13C, 14C, 15C, 16C, 17C, 18C, and 19C show the planardistribution of electron density distribution Ne, wherein ΔNe denotes avalue in percentage terms obtained where the difference between theplanar maximum value and minimum value of Ne is divided by the double ofthe planar mean value of Ne.

As shown in these figures, it was confirmed that, where a voltage wasapplied to the segments according to the embodiment shown in FIG. 1, theplanar distribution of plasma potential Vf, planar distribution ofself-bias voltage Vdc, and planar distribution of electron densitydistribution Ne could be adjusted and controlled. Particularly, in thecase shown in FIGS. 14A, 14B, and 14C where the RF power was set at 500W, the inner segment was grounded, and the outer segment was suppliedwith the DC voltage at different voltage values, all the planardistributions of Vf, Vdc, and Ne were uniformized when the DC voltagewas at −100V. Further, in the case shown in FIGS. 15A, 15B, and 15Cwhere the RF power was set at 500 W, the outer segment was grounded, andthe inner segment was supplied with the DC voltage at different voltagevalues, all the planar distributions of Vf, Vdc, and Ne were uniformizedwhen the DC voltage was at +40V.

Next, an experiment was conducted where the inner segment was suppliedwith the DC voltage at different voltage values, while no voltage wasapplied from a distribution control power supply, to measure the planardistribution of plasma potential Vf. The RF power was set at differentvalues of 200 W and 500 W, and the other conditions were set to be thesame as those in the experiment described above.

FIGS. 20A and 20B show data obtained in this experiment. FIG. 20A showsthe planar distribution of plasma potential Vf relative to the groundpotential (GND) where the RF power was set at 200 W, and the innersegment was supplied with the DC voltage at different voltage values of+50V, −36V, and −120V. FIG. 20B shows the planar distribution of plasmapotential Vf relative to the ground potential (GND) where the RF powerwas set at 500 W, and the inner segment was supplied with the DC voltageat different voltage values of +10V, −56V, and −120V. As shown in thesefigures, it was confirmed that, where the voltage of the other DC powersupply was changed, the degree of Vf was adjustable while thedistribution pattern of Vf was essentially maintained.

The present invention is not limited to the embodiments described above,and it may be modified in various manners. For example, in theembodiments described above, the segments are disposed on the lowersurface of the upper electrode through an insulating film to define apart of the ceiling of the process chamber 1. In this respect, FIG. 21is a view schematically showing another example of an upper electrode.In this example, an upper electrode 118 comprising an inner segment 118a and an outer segment 118 b is disposed separately from the ceiling ofa process chamber 1. In this case, the inner segment 118 a and outersegment 118 b may be arranged to form a mesh.

In the embodiments described above, the segments are concentricallydisposed, but they may be not necessarily concentric. Further, in theembodiments described above, the number of segments is two or three, butit may be four or more. In the embodiment shown in FIGS. 10 and 11, thesegments 18 _(c3) and 18 _(c4) connected to one of the terminals of theDC power supply can be switched therebetween. Alternatively or further,the segment 18 _(c5) connected to the other of the terminals may be alsodivided into two portions and configured to be switched therebetween.The embodiment shown in FIGS. 10 and 11 may be combined with thestructures shown in FIGS. 7A, 7B, 8, and 9.

In the embodiments described above, the ring magnets are used to form amagnetic field around the process space. Each of the ring magnets has aplurality of segment magnets formed of permanent magnets and disposedaround the chamber to be a ring in a multi-pole state. However, suchmagnetic field forming means is not necessarily required. Further, inthe embodiments described above, the present invention is applied toplasma etching, but it may be applied to another plasma process, such asplasma CVD or sputtering. Similarly, other apparatus components, thematerial of the conductive layer, and so forth are not limited to thoseof the embodiments described above, and they may be modified in variousmanners. Furthermore, in the embodiments described above, the targetsubstrate is a semiconductor wafer, but it may be applied to anothersubstrate for, e.g., flat panel displays (FPDs), such as LCDs.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A capacitive coupling plasma processing apparatus comprising: aprocess chamber configured to have a vacuum atmosphere; a process gassupply section configured to supply a process gas into the chamber; alower electrode disposed in the chamber and configured to support atarget substrate thereon; an upper electrode disposed opposite the lowerelectrode in the chamber, and including a plurality of conductivesegments separated from each other and facing the lower electrode; aradio frequency (RF) power supply connected to the lower electrode toapply an RF power to the lower electrode to form an RF electric fieldwithin a plasma generation region between the lower and upperelectrodes, so as to turn the process gas into plasma by the RF electricfield; and a direct current (DC) power supply configured to apply a DCvoltage to at least one of the segments of the upper electrode, whereinthe segments include an inner segment and an outer segment disposedaround and separated from the inner segment, the DC power supply beingconfigured to apply the DC voltage to a least one of the inner and outersegments, and the segments further include a middle segment disposedbetween and separated from the inner segment and the outer segment, themiddle segment being configured to be selectively supplied with a DCvoltage.
 2. The apparatus according to claim 1, wherein the inner,middle, and outer segments are concentrically disposed.
 3. The apparatusaccording to claim 2, wherein the upper electrode further includes agrounded conductive common base, and the inner, middle, and outersegments are supported side by side by the common base through a planateinsulating film such that the inner, middle, and outer segments face thelower electrode.
 4. The apparatus according to claim 3, wherein lowerfaces of the inner, middle, and outer segments are present on a sameplane.
 5. The apparatus according to claim 3, wherein the common basehas a gas diffusion space formed therein to receive the process gas, anda plurality of gas delivery holes are formed in the common base, theinsulating film, and the segments to derive the process gas from the gasdiffusion space to the plasma generation region.
 6. The apparatusaccording to claim 1, wherein the DC power supply is configured to applythe DC voltage to cause the inner segment to have an electric potentialhigher than that of the outer segment.
 7. The apparatus according toclaim 6, wherein the process chamber is grounded and the electricpotential of the inner segment is a positive electric potential.
 8. Theapparatus according to claim 1, wherein the RF power applied from the RFpower supply to the lower electrode has a frequency of 27 MHz to 160MHz.
 9. The apparatus according to claim 8, wherein the upper electrodeis not connected to any RF power supply.
 10. The apparatus according toclaim 1, wherein the DC power supply is a variable DC power supply. 11.The apparatus according to claim 9, wherein the variable DC power supplyis a bipolar power supply.
 12. The apparatus according to claim 1,wherein the DC power supply is connected to at least one of the innerand outer segments through an ON/OFF switch.
 13. The apparatus accordingto claim 1, wherein the DC power supply is connected to at least one ofthe inner and outer segments through a low-pass filter.
 14. Theapparatus according to claim 1, wherein the DC power supply has positiveand negative terminals, one of which is connected to one of the inner,middle, and outer segments, and the other terminal is connected to andswitchable between the other two of the inner, middle, and outersegments.
 15. The apparatus according to claim 14, wherein the negativeterminal of the DC power supply is connected to the outer segment, andthe positive terminal of the DC power supply is connected to andswitchable between the inner and middle segments.
 16. The apparatusaccording to claim 15, wherein the negative terminal of the DC powersupply is connected to the outer segment through an ON/OFF switch, andthe positive terminal of the DC power supply is connected to the innerand middle segments respectively through ON/OFF switches.
 17. Theapparatus according to claim 14, wherein the DC power supply isconnected to each of the inner, middle, and outer segments through alow-pass filter.
 18. The apparatus according to claim 1, wherein theprocess gas supply section is configured to supply, as the process gas,an etching gas for etching the target substrate.
 19. The apparatusaccording to claim 18, wherein the apparatus further comprises a controlsection configured to control an operation of the apparatus andincluding a non-transitory storage medium storing a control program,which, when executed, causes the control section to control theapparatus to conduct an sequence of turning the etching gas into plasmainside the process chamber to etch the target substrate by use of theplasma, while setting the inner segment to have an electric potentialhigher than that of the outer segment by the DC power supply, so as touniformize spatial electric potential distribution within the plasmageneration region.
 20. The apparatus according to claim 18, wherein theetching gas contains a halogen-containing gas or O₂ gas.